I ask because I have a Tokina 28-80AT-X Pro f 2.8 and the images aren't right on my 5DII.

I purchased the lens used and sent it off to Tokina to be checked out. It was sent back to me as OK, but there was a note on the work order that the optical formula for digital camera lenses is different (can't remember the exact wording).

I messed with it a little yesterday, and it seems that the lens may just be front focusing. I'll need to try some more tests when I have some time.

One issue relates to angle of incidence - the angle at which rays strike the sensor.

Film responds to oblique rays (those that do not strike at right angles) proportionately to the cosine of the angle of incidence (which is measured with respect to arrival at right angles). This is one ingredient in the fall-off of effective exposure for off-axis parts of the scene (natural vignetting), as well as a loss of effective exposure even for on-axis scene points in the case of a large-aperture lens..

With a typical digital sensor, the fall-off in response may be faster than as the cosine of the angle, thus exacerbating the fall-off in effective exposure. The problem is most pronounced in wide-angle lenses.

To mitigate this, in lenses intended to be usable in digital cameras, design schemes are often used than decrease the maximum obliquity of the rays. These include the so-called quasi-telecentric designs, in which the exit pupil of the lens is quite far forward.

The bottom line is that wide-angle lenses (in particular) not specially designed for use with digital cameras may exhibit more off-axis fall-off, and more "shortfall" of effective exposure at large apertures, than we might wish.

Another issue is that digital cameras may be more susceptible to internal reflections caused by rays bouncing between the sensor and various lens surfaces. For that reason, in lenses specifically intended to be usable with digital cameras, special attention may be given to anti-reflective coating and the curvature of critical lens surfaces.

For that reason, lenses not having that design attention, when used on a digital camera, may exhibit more loss of contrast (through "flare") or even overt "sun dogs" than when used on a film camera.

I still have my two original EF lens I bought with my EOS650 in 1987. They are an 35-105mm f3.5-4.5 and a 70-210mm f4.0. Both are push-pull zooms, surprising clean considering all the nasty things one reads about push-pulls. And both are still working perfectly on my Canon digital cameras. My daughter has stolen the 35-105 and uses it on her Rebel T2i. I still use the 70-210 lens on my 7D. Both are capable of taking nice sharp pictures especially the 70-210. You have to love a company that makes a product that still works perfectly 24 years after you bought it.

Old lenses work fine optically on digital cameras, but are not as good as those designed for digital. However, you are talking autofocus issues, and the lens may need adjustment, or the camera body, or both.

Old sigma lenses would not work at all on Canon Digital SLR's until they modified them. Then the next new Canon model came out, and they failed to work on it. Tokina and Tamron did a good job of reverse engineering the Canon AF system, and all their EOS compatible lenses are capable of focusing properly on a Canon DSLR.

Just be sure to actually take test photos before buying a old Sigma or Quantaray or any other older rebranded lens, since Sigma will not fix them.

+1. It depends on the lens, but recently I've been using a lot older MF lenses with an Olympus EPL-1. My 24mm lens which I normally consider superb is very average. But as move towards the telephoto end, the results improve dramatically.

My 17-40 also seems to work better with film than digital. I've often wondered if this is for the same reason.

Just because your lens is compatible with a digital camera, it doesn't necessarily follow that it is optimized for digital. Over the last ten years, many lenses have had minor design tweaks to make them work better with DSLRs.

I ask because I have a Tokina 28-80AT-X Pro f 2.8 and the images aren't right on my 5DII.

I purchased the lens used and sent it off to Tokina to be checked out. It was sent back to me as OK, but there was a note on the work order that the optical formula for digital camera lenses is different (can't remember the exact wording).

I messed with it a little yesterday, and it seems that the lens may just be front focusing. I'll need to try some more tests when I have some time.

Thanks for any input.

I use the 20mm, 28mm, 35mm, 50mm AIS or AI Nikkor primes for my 5D Mark II, they work great because everything I do whether it's photography or video is done in manual. In my opinion the older primes with the metal bodies are better made than Nikons newer plastic ones these days. I recently purchased an nikon 85mm 1.8 and that plastic junk broke after a months use. The AIS models are 20 plus years old and have never had a problem.